Suppression of Cross-Polarized Radiation of Rectangular Microstrip Antenna on Slot-Type Defected Ground Using Periodic Circular Structure

A novel resonant-type defected ground structure (DGS) featuring a modified internal structure is proposed to enhance the suppression of cross-polarized (XP) radiation of rectangular microstrip antennas (RMAs) on slot-type DGS. Specifically, integrating periodic circular metal structure (PCS) into the slot-type DGS, which has been demonstrated to reduce RMA XP levels and minimize the space occupied by defects. As a resonant-type DGS, the embedding of the PCS enables the excitation of the entire DGS by the fringe field of the patch. The coupling between the fringe field and the PCS-type DGS results in a significant alteration of the field distribution of the high-order mode TM02, thereby effectively suppressing the XP radiation generated by TM02 mode. This structural concept originates from the unique control capabilities of periodic structures over electromagnetic field propagation, with the objective of optimizing the symmetry of the substrate field distribution inside the defect region. Compared to slot-type DGS, the periodic structure enables more electromagnetic fields to couple into the slot from the non-radiating side and disperse among each metal element, generating resonance in the TM02 mode field. Experiments demonstrate the H-plane co-cross polarization isolation exceeds 25 dB across an azimuth range exceeding 200°, with peak XP suppression reaching 20 dB. This performance is at the forefront of resonant-type DGSs.